Material for lithium battery positive electrode and production thereof

ABSTRACT

The material for a lithium battery positive electrode of the present invention is characterized in that a powder of an active material comprising at least one member selected from the group consisting of lithium phosphates, lithium-cobalt phosphates, cobalt oxides and lithium-cobalt oxides, wherein lithium, cobalt and phosphorus are contained in a proportion of more than 0.1 mole of cobalt and more than 0.2 mole of phosphorus both per mole of lithium, is formed into a sheet using a binder comprising an organic polymer, and the present invention affords a material for a lithium battery positive electrode, which is superior in practical use and production efficiency, without impairing the high electromotive force of the novel active material having the aforementioned composition. The production method of the present invention is characterized by extending a binder solution comprising a powder of the above-mentioned active material on a long support sheet, and drying, and affords a long material for a lithium battery positive electrode stably and efficiently by a continuous process.

TECHNICAL FIELD

The present invention relates to a material, in a sheet form, for alithium battery positive electrode, which is advantageously used forforming a cylindrical secondary battery having a high electromotiveforce, and the production of such long sheet.

BACKGROUND ART

There have been known, as positive electrodes capable of forming alithium battery having a high electromotive force, positive electrodesusing LiCoO₂ as an active material. The group of the present inventorshas found an active material comprising at least one member selectedfrom the group of lithium phosphates, lithium-cobalt phosphates, cobaltoxides and lithium-cobalt oxides, wherein lithium, cobalt and phosphorusare contained in a proportion of more than 0.1 mole of cobalt and morethan 0.2 mole of phosphorus both per mole of lithium.

The novel active material having the composition as mentioned above ischaracterized in that it also comprises phosphorus besides lithium,cobalt and oxygen. The addition of phosphorus leads to a less mass andincreases lithium ion incorporation per unit weight, which ultimatelyresults in increased capacities. By using said active material for apositive electrode, primary or secondary lithium batteries superior inelectromotive force, discharge voltage, discharge capacity and energydensity, and having a still higher electromotive force than theconventional batteries using LiCoO₂, can be obtained.

DISCLOSURE OF THE INVENTION

In general terms, batteries have greatly diverse properties depending onthe combination of starting materials, which is possibly due tomicroelectric chemical reactions they undergo. Accordingly, practicalbatteries are made to exhibit the specific properties they have bydeliberately balancing the respective materials. When the maincomponents are changed, therefore, new materials should be developed, sothat a battery capable of exhibiting the properties based on the newmain components can be fabricated.

The present invention aims at providing a material for a positiveelectrode of a lithium battery, which is superior in practical use andproduction efficiency, without impairing the high electromotive forceafforded by the aforementioned novel active material.

The present invention provides a material for lithium battery positiveelectrodes, characterized in that a powder of an active materialcomprising at least one member selected from the group consisting oflithium phosphates, lithium-cobalt phosphates, cobalt oxides andlithium-cobalt oxides, wherein lithium, cobalt and phosphorus arecontained in a proportion of more than 0.1 mole of cobalt and more than0.2 mole of phosphorus both per mole of lithium, is formed into a sheetusing a binder comprising an organic polymer, and a method for producinga material for a lithium battery positive electrode, which ischaracterized by extending a binder solution comprising a powder of theabove-mentioned active material, on a long support sheet, and drying.

By using the positive electrode material of the construction asmentioned above, a material, in a sheet form, for lithium batterypositive electrodes, which is superior in practical use and productionefficiency, can be provided without impairing the high electromotiveforce of a novel active material having the above-mentioned composition.According to the production method mentioned above, a long sheet forlithium battery positive electrodes can be stably and efficientlyobtained by a continuous process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an embodiment of a positive electrodematerial.

FIG. 2 is a sectional view of another embodiment of a positive electrodematerial.

FIG. 3 is a schematic sectional view showing a production of a positiveelectrode material.

FIG. 4 is a sectional view showing one example of the structure of abattery.

FIG. 5 is a schematic sectional view showing another production of apositive electrode material.

FIG. 6 is a schematic sectional view showing a still another productionof a positive electrode material.

FIG. 7 is a sectional view showing another example of the structure of abattery.

FIG. 8 is a schematic sectional view showing a still another productionof a positive electrode material.

FIG. 9 is a graph showing the discharge property of a battery comprisingthe positive electrode materials prepared in Examples 1-7 andComparative Example.

DETAILED DESCRIPTION OF THE INVENTION

One example of the material for lithium battery positive electrodes ofthe present invention is shown in FIG. 1, wherein 1 is a layercontaining an active material powder held by a binder and 2 is a supportsheet.

As the above-mentioned lithium phosphate, exemplified are salts oflithium with phosphoric acid such as metaphosphoric acid, pyrophosphoricacid, orthophosphoric acid, triphosphoric acid and tetraphosphoric acid,with preference given to a salt of lithium with orthophosphoric acid.Examples of the lithium-cobalt phosphate include Li₂ CoPO₅, LiCoPO₄,LiCo₀. 9 P₀. 1 O₂ and LiCo₀. 5 P₀. 5 O₂, with preference given toLiCoPO₄. Examples of the cobalt oxide include CoO, Co₂ O₃, CoO₂ and Co₃O₄, with preference given to Co₃ O₄. Examples of lithium-cobalt oxideinclude LiCoO₂, Li₆ CoO₄, Li₀. 73 CoO₂ and Li₀. 63 CoO₂, with preferencegiven to LiCoO₂.

The novel active material comprises at least one member selected fromthe group consisting of lithium phosphates, lithium-cobalt phosphates,cobalt oxides and lithium-cobalt oxides, wherein lithium, cobalt andphosphorus are contained in a proportion of more than 0.1 mole of cobaltand more than 0.2 mole of phosphorus both per mole of lithium. They maybe used alone or in combination, as long as they satisfy said molarratio.

That is, lithium-cobalt phosphate may be used alone, or cobalt oxide,and lithium phosphate or lithium-cobalt phosphate in two kinds ofcombinations; cobalt oxide and other two materials in three kinds ofcombinations; or a mixture of the four may be used. Of these, a mixtureof three or more kinds of the compounds is preferable, since a lithiumbattery having a high electromotive force can be obtained thereby.Particularly preferred is a mixture containing the three kinds of atleast cobalt oxide, lithium phosphate and lithium-cobalt phosphate.

When producing the novel active material, each transition metal such asnickel, iron, manganese, chromium and vanadium, oxide thereof, hydroxidethereof, salt thereof such as carbonate, nitrate and organic acid salt,or organic compound thereof may be added. In this case, a compoundwherein part of cobalt of the above-mentioned cobalt-containing compoundis substituted by the aforementioned transition metal is produced.

When producing the novel active material, it is essential that thepredetermined amounts of respective starting materials be added, so thatthe amount of cobalt is more than 0.1 mole and that of phosphorus ismore than 0.2 mole, both per mole of lithium, preferably 0.2-0.75 moleof cobalt and 0.25-1.8 moles of phosphorus, both per mole of lithium,whereby a lithium phosphate and/or lithium-cobalt phosphate are/isprepared.

When the molar number of cobalt is not more than 0.1 per mole oflithium, charging is unattainable, whereas that of more than 0.75results in undesirable small capacity. On the other hand, when thephosphorus is not more than 0.2 mole, the above-mentioned phosphate isnot produced sufficiently, whereas the amount exceeding 1.8 molesresults in insufficient formation of the above-mentioned phosphate, dueto the relatively decreased amount of lithium, thus leading to anundesirably less discharge voltage.

The novel active material is prepared by an appropriate method forproducing ceramic, such as solid phase method, sintering method, sol-gelmethod, CVD method, PVD method, thermal spraying method and thermaldecomposition method. The powder of the novel active material can beobtained by, for example, pulverizing the powder produced in the above,according to an appropriate method such as by using a ball mill. Whilethe particle size of the powder is determined as appropriate accordingto the object of use, it is generally not more than 100 μm in terms ofthe surface area of the electrode thus formed, with preference given tonot more than 50 μm, particularly not more than 20 μm.

The material for a lithium battery positive electrode of the presentinvention can be formed by retaining the powder of the novel activematerial in a sheet form using a binder. Accordingly, the binder shouldbe able to retain the sheet form by cohering the powder of the novelactive material. When a battery having a structure, wherein a positiveelectrode is immersed in an electrolyte solution, is desired, a bindercapable of retaining the cohesion of the powder of the novel activematerial in the electrolyte solution is used.

Generally used as the binder is an organic polymer. Examples of thepolymer are various polymers conventionally used, which are typicallythermoplastic polymers such as ethylene-propylene-diene terpolymer,acrylonitrile polymer, fluororesin and polyethylene. In addition,appropriate thermosetting polymers such as heat-curing acrylic polymersare exemplified.

The binder preferably used in relation to the novel active material is afluororesin which is exemplified by homopolymers of a kind of monomerhaving at least one carbon-fluorine bond on the main chain or branchedchain and copolymers of two or more members selected from the group ofthe aforementioned monomers and oligomers.

Examples of the above-mentioned fluororesin includepolytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinylether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer(FEP), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinylether copolymer (EPE), tetrafluoroethylene-ethylene copolymer (ETFE),poly(vinyl fluoride) (PVF), polyhexafluoropropylene, poly(vinylidenefluoride) (PVDF) and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer.

The positive electrode material of the present invention has a structurewherein the powder of a novel active material is homogeneously dispersedin a binder, and optionally contains a conductivity-imparting substancesuch as carbon black. The positive electrode material can be produced bya dry method, a wet method or other methods. In the dry method, thenecessary constituent materials are mixed and kneaded in a twin-rollmill, Bambury mixer and the like, and formed into a desired sheet byextrusion forming using a T die.

In the wet method, a powder of the novel active material is dispersed ina liquid obtained by dissolving or dispersing an organic polymer in anorganic solvent, water and the like (hereinafter the final liquid isreferred to as binder solution) and the binder solution is applied to asuitable support sheet and dried to give a desired sheet.

When producing a positive electrode material, the binder solution isused in the form of a paste or a dispersion. In the present invention, apaste is preferable in terms of easiness of forming sheets.

While the binder solution is applied by an optional method, it isadvantageously applied continuously by, for example, doctor blademethod, roll forming method, dipping method, spray method and the like,to a long support sheet, while moving the sheet using a sieve and thelike, in consideration of the stable and efficient forming of a longsheet by a continuous process.

The above-mentioned binder solution is prepared by homogeneouslydispersing a powder of a novel active material in a solution ordispersion obtained by dissolving or dispersing the aforementionedorganic polymer in, for example, a suitable organic solvent such ascyclohexane (CyH), dimethylformamide (DMF) and N-methyl-2-pyrrolidone(NMP), or water.

When the organic polymer is insoluble in water or organic solvent, likePTFE, a powder of a novel active material can be dispersed in adispersion obtained by dispersing a micropowder of the polymer in wateror an organic solvent. In the present invention, however, the use of anorganic solvent, rather than water, for a binder solution isparticularly preferable for the reasons set forth below.

That is, the positive electrode material needs to be dried afterforming. In general, water is difficult to remove in comparison withorganic solvents, and is industrially disadvantageous. In addition, theresidual water due to insufficient dehydration possibly results inincrease of overvoltage by the reaction thereof with a positiveelectrode material, negative electrode material or electrolyte in thebattery; corrosion of metals in the battery; and degraded batteryperformance due to the electrolysis of the residual water. When water isused, therefore, sufficient drying, such as by heating in vacuo, isrecommended to make the residual water content not more than 0.1% byweight, particularly not more than 0.01% by weight.

When an organic solvent is used, removing of the solvent is markedlyeasier than water. The problems caused by residual solvent are less andthe degree of the adverse influence is far smaller than that caused bythe residual water.

In the present invention, the residual organic solvent content is notmore than 1% by weight, preferably not more than 0.1% by weight.

In the present invention, an organic polymer soluble in an organicsolvent is preferably used for the reasons stated above, andparticularly preferred is a fluororesin from the aspect of chemicalstability. Specifically, poly(vinylidene fluoride) (PVDF) is preferable,in that it causes small overvoltage, can dissolve in many organicsolvents, permitting easy paste forming, and is superior in bindingproperty, making the PVDF content smaller when forming a positiveelectrode sheet.

The organic solvent to be used for preparing the above-mentioned bindersolution is preferably N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide(DMSO), γ-butyrolactone (γ-BL), propylene carbonate (PC), ethylenecarbonate (EC), dimethylformamide (DMF) and the like, in which theabove-mentioned fluororesin can be dissolved. In particular, NMP andDMSO can lower the viscosity of the binder solution and are superior informability when using, for example, a doctor blade.

The proportions of the powder of a novel active material and an organicpolymer may be appropriately determined depending on the cohesion ofsaid powder. In general, an organic polymer is used in a proportion of0.1-20 parts by weight, preferably 1-5 parts by weight per 100 parts byweight of the powder of the novel active material.

The content of the solid in the binder solution is appropriatelydetermined depending on the flowability necessary for the coatingmethod. The binder solution generally has a solid content of 1-70% byweight. The binder solution may further contain suitable substances suchas a conductive material (e.g. acetylene black and ketzen black)depending on the desired material for a lithium battery positiveelectrode.

The support sheet to be applied with the above-mentioned binder solutionmay be formed from appropriate materials such as releasing paper andconductive sheets, such as aluminum sheet and copper sheet. Thereleasing paper is preferable when moving a positive electrode materialformed thereon onto another support material.

A conductive sheet can be preferably used when it is utilized as amaterial for a positive electrode having a collector layer. Theconductive sheet generally has a non-limiting thickness of 5-300 μm.While the conductive sheet is generally a metal sheet, a conductiveplastic sheet may be also used and the material thereof is notparticularly limited.

The thickness of the positive electrode material to be formed on theabove-mentioned support sheet is generally, but not limited to, 5-500μm, particularly 50-300 μm, and the thickness can be determined asappropriate in the present invention, according to the object of use.

In the present invention, moreover, a layer 1 containing an activematerial powder, which is shape-retained on the both sides of a supportsheet 2 with a binder, can be also formed, as shown in FIG. 2.

The positive electrode material of the present invention is used forforming a positive electrode of a primary or secondary lithium battery,and the electrode can be formed into a suitable form using the sheet,according to the mode of the desired lithium battery. For example, along sheet may be wound to form a cylindrical battery or formed into anappropriate size to manufacture a laminate type square battery. As thenegative electrode of the lithium battery, lithium, alloy thereof,carbon and other suitable materials can be used.

PREPARATIVE EXAMPLE 1

Lithium carbonate, basic cobalt carbonate, and a 85% aqueous solution ofphosphoric acid were mixed at an atomic ratio of Li:Co:P=2:1:1, and themixture was placed in an alumina crucible. The mixture was heated at900° C. for 24 hours in an electric furnace to give an oxide. The oxidewas subjected to a powder X-ray diffraction analysis and identifiedagainst JCPDS card (hereinafter the same procedure was taken). The oxidewas found to be a mixture of lithium phosphate, lithium-cobalt phosphateand cobalt oxide, containing 0.5 mole of cobalt and 0.5 mole ofphosphorus per mole of lithium. The oxide was pulverized in a ball millto give an active material powder having a particle size of not morethan 20 μm.

PREPARATIVE EXAMPLE 2

In the same manner as in Preparative Example 1 except that lithiumcarbonate, basic cobalt carbonate, and a 85% aqueous solution ofphosphoric acid were used so that the atomic ratio of Li:Co:P was1:0.4:1.6, a mixture of lithium phosphate, lithium-cobalt phosphate andcobalt oxide was obtained. An active material powder having a particlesize of not more than 20 μm was obtained from the mixture. The activematerial contained 0.4 mole of cobalt and 1.6 moles of phosphorus permole of lithium.

PREPARATION EXAMPLE 3

In the same manner as in Preparative Example 1 except that lithiumcarbonate, basic cobalt carbonate, and a 85% aqueous solution ofphosphoric acid were used so that the atomic ratio of Li:Co:P was1:1:0.4, a mixture of lithium phosphate, lithium-cobalt phosphate andcobalt oxide was obtained. An active material powder having a particlesize of not more than 20 μm was obtained from the mixture. The activematerial contained 1.6 moles of cobalt and 0.4 mole of phosphorus permole of lithium.

EXAMPLE 1

Polyvinylidene fluoride (2 parts, part by weight, hereinafter the same,manufactured by Aldrick Chemical Co., US, Product number 18720-2) wasdissolved in N-methyl-2-pyrrolidone (98 parts). The active materialpowder (90 parts) as obtained in Preparative Example 1 and acetyleneblack (8 parts) were added and mixed to give a paste dispersion.

As shown in FIG. 3, the above-mentioned dispersion 6 was set on theupper portion of a support table 5 and continuously applied to analuminium sheet (collector) 3 having a width of 50 mm and a thickness of0.02 mm by the doctor blade method, while continuously delivering thealuminum sheet on the support table at a rate of 1 m/min via a sieve 4having a diameter of 400 mm, and the thickness of the coating wasadjusted by a doctor blade 7. The sheet was led into a drying furnace 8(150° C., 1 m length) and dried, whereafter the sheet was wound on asieve 10 having a diameter of 400 mm to continuously give a 0.1 mm thickpositive electrode material 9 (a layer containing a novel activematerial powder).

In the above, the sieve 4 for delivering and the sieve 10 for taking upwere synchronized to relax the tension applied to the aluminum sheet.The diameter of the winding sieve 10 was determined such that crackswould not be developed in the layer containing the powder of the novelactive material.

As shown in FIG. 4, a positive electrode (5 cm×5 cm) formed from thepositive electrode material 9 obtained in the above was placed on anegative electrode 12 (5 cm×5 cm) of metallic lithium on a nickel 13,via a separator 11 (6 cm×6 cm) comprising a micro-cellular polypropylenesheet, and immersed in an electrolyte solution 14 obtained by dissolving1 mole of LiClO₄ in 100 parts of a mixed solvent of propylene carbonateand 1,2-dimethoxyethane (volume ratio=1:1) to manufacture a beaker cell.In the Figure, 15 is a beaker, 16 is a sealing plug made from a siliconerubber, and 17 and 18 are lead wires for positive and negativeelectrodes.

EXAMPLE 2

As shown in FIG. 5, the dispersion 6 obtained according to Example 1 wasformed into a 0.8 mm×50 mm sheet via a nozzle 19 and supplied on a roll21 by the roll forming method at a rate of 200 mm/min, whilecontinuously delivering an aluminum sheet 3 (width 50 mm, thickness 0.02mm) downward between counter-opposite rolls 20 and 21 at a rate of 1.6m/min, to continuously apply the dispersion to the aluminum sheet viathe counter-opposite rolls, whereafter the sheet was led into a dryingfurnace 8 (150° C., 1 m length), dried, wound on a sieve 10 having adiameter of 400 mm to continuously give a 0.1 mm thick positiveelectrode material 9. Using the material obtained, a beaker cell wasmanufactured according to Example 1.

EXAMPLE 3

As shown in FIG. 6, an aluminum sheet 3 (width 50 mm, thickness 0.02 mm)was delivered into a tank 24 containing the dispersion 6 obtainedaccording to Example 1, at a rate of 1 m/min via a sieve 22 having adiameter of 200 mm, and the sheet was turned via a sieve 23 (200 mmdiameter) to take out the sheet from the tank, whereby a dispersion wasapplied to the both sides of the aluminum sheet by the dipping method.The sheet was passed through a die 25 to adjust the coating thickness,led into a drying furnace 8 (150° C., 1 m length), dried, wound on asieve 27 having a diameter of 500 mm to continuously give a positiveelectrode 26 of an aluminum sheet carrying a 0.1 mm thick positiveelectrode material on the both sides. The respective sieves were rotatedin a synchronized manner.

As shown in FIG. 7, a positive electrode 26 (5 cm×2.5 cm) formed abovewas placed in between negative electrodes 29 (5 cm×2.5 cm) of a metalliclithium formed on a nickel 30, via separators 28 (6 cm×3 cm) comprisinga micro-cellular polypropylene sheet, and immersed in an electrolytesolution 14 obtained according to Example 1 to give a beaker cell. Inthe Figure, 31 is a beaker, 16 is a sealing plug made from a siliconerubber, and 32 and 33 are lead wires for positive and negativeelectrodes.

EXAMPLE 4

An ethylene-propylene-diene terpolymer (2 parts, manufactured by AldrickChemical Co., US, Product number 20051-4) was dissolved in cyclohexane(400 parts). The novel active material powder (90 parts) as used inExample 1 and acetylene black (8 parts) were added and mixed to give adispersion.

As shown in FIG. 8, the above-mentioned dispersion 36 was continuouslysprayed on an aluminum sheet 3 (width 50 mm, thickness 0.02 mm) on asupport table 35 heated to 80°-100° C., by the spray method using aspray nozzle 37 and a nitrogen gas, while delivering the aluminum sheetdownward at a rate of 1 m/min via a sieve 34 having a diameter of 100mm. The solvent was allowed to immediately evaporate on the heatedsupport table to adhere the solid. The thickness was adjusted usingcrimp rolls 39 and 40, whereafter the sheet was led into a dryingfurnace 8 (150° C., 1 m length), dried, wound on a sieve 42 having adiameter of 300 mm to continuously give a 0.1 mm thick positiveelectrode material 41. According to Example 1, a beaker cell was formedusing the material. In the Figure, 38 is a nitrogen bomb.

EXAMPLE 5

A vinylidene-hexafluoropropylene-tetrafluoroethylene copolymer (2 parts,Trademark Dai-el G501, manufactured by DAIKIN INDUSTRIES LTD.) wasdissolved in dimethylformamide (98 parts). The novel active materialpowder (90 parts) as used in Example 1 and acetylene black (8 parts)were added and mixed to give a paste dispersion. Using the dispersion, apositive electrode material was formed, and a beaker cell wasmanufactured using the material.

EXAMPLE 6

An acrylonitrile polymer (2 parts, Trademark CYANORESIN, manufactured byShin-Etsu Chemical Company Ltd.) was dissolved in dimethylformamide (98parts). The novel active material powder (90 parts) as used in Example 1and acetylene black (8 parts) were added and mixed to give a pastedispersion. According to Example 1, a positive electrode material wasformed using the dispersion, and a beaker cell was manufactured usingthe material.

EXAMPLE 7

An ethylene-propylene-diene terpolymer (2 parts) as used in Example 4was dissolved in cyclohexane (98 parts). The novel active materialpowder (90 parts) as used in Example 1 and acetylene black (8 parts)were added and mixed to give a paste dispersion. According to Example 1,a positive electrode material was formed using the dispersion, and abeaker cell was manufactured using the material.

COMPARATIVE EXAMPLE

Lithium carbonate and basic cobalt carbonate were mixed at an atomicratio of Li:Co=1:1, and the mixture was placed in an alumina crucible.The crucible was heated at 900° C. for 24 hours in an electric furnaceto give a lithium-cobalt compound oxide (active material). The oxide waspulverized in a ball mill to give a powder having a particle size of notmore than 20 μm. The active material was analyzed by a powder X-raydiffraction analysis and was found to match JCPDS card No. 16-427.

In the same manner as in Example 1 except that the aforementioned activematerial powder was used instead of the novel active material as used inExample 1, a positive electrode material was obtained and a beaker cellwas manufactured using the material.

Evaluation test

The beaker cells obtained in the above Examples and Comparative Examplewere charged with a constant current of 0.5 mA/cm² and discharged at 0.5mA/cm². Discharge property was examined, the results of which are shownin FIG. 9.

According to FIG. 9, the cells of Examples are superior to the cell ofComparative Example in discharge voltage and discharge capacity.

EXAMPLES 8-16

The novel active materials, binders and solvents were combined invarious ways as shown in the following Table, and positive electrodematerials were obtained according to Example 1. Using the materials,beaker cells were manufactured. In every Example, used were a solvent(97 parts), a binder (3 parts), a powder of active material (90 parts)and acetylene black (7 parts).

When the binder was PTFE, an aqueous dispersion thereof (TrademarkPolyflon TFE dispersion, manufactured by DAIKIN INDUSTRIES LTD.) wasdiluted as necessary with distilled water.

The positive electrode material obtained using the above-mentioned PTFEwas dehydrated by drying at 200° C. under reduced pressure for 1 week toadjust the residual water content in the positive electrode material toabout 0.01% by weight. The positive electrode material obtained using anorganic solvent was dried at 120° C. under reduced pressure for 3 hoursto remove the solvent, thereby adjusting the residual solvent content inthe positive electrode material to about 0.1% by weight.

The beaker cells obtained in the above Examples 8-16 were subjected tothe measurement of overvoltage at 0.5 mA/cm² constant current, theresults of which are summarized in the Table. In every Example,particularly when a fluororesin binder is used, overvoltage wasespecially small and battery capacity was high.

    ______________________________________                                        novel active                                                                  material      binder   solvent overvoltage (V)                                ______________________________________                                        Ex. 8  Prep. Ex. 1                                                                              PVDF     NMP   0.020                                        Ex. 9  Prep. Ex. 2                                                                              PVDF     NMP   0.022                                        Ex. 10 Prep. Ex. 3                                                                              PVDF     DMF   0.025                                        Ex. 11 Prep. Ex. 1                                                                              PTFE     water 0.015                                        Ex. 12 Prep. Ex. 2                                                                              PTFE     water 0.018                                        Ex. 13 Prep. Ex. 3                                                                              PTFE     water 0.020                                        Ex. 14 Prep. Ex. 1                                                                              PFA      DMF   0.032                                        Ex. 15 Prep. Ex. 1                                                                              EPDM     CyH   0.08                                         Ex. 16 Prep. Ex. 1                                                                              AcNP     DMF   0.12                                         ______________________________________                                         PVDF: poly(vinylidene fluoride)                                               NMP: Nmethyl-2-pyrrolidone                                                    DMF: dimethylformamide                                                        PTFE: polytetrafluoroethylene                                                 PFA: tetrafluoroethyleneperfluoroalkyl vinyl ether copolymer                  EPDM: ethylenepropylene-diene terpolymer                                      CyH: cyclohexane                                                              AcNP: acrylonitrile polymer (CYANORESIN)                                 

Using the material for a positive electrode of the present invention, apositive electrode in a sheet form, comprising a novel active material,can be obtained, and a lithium battery superior in practical use, havingexcellent electromotive force, discharge voltage and discharge capacity,can be obtained. In addition, a long material for the positive electrodecan be obtained stably and efficiently by a continuous process,according to the production method of the present invention.

What is claimed is:
 1. A material for a lithium battery positiveelectrode in the form of a sheet comprising an organic binder and apowdery active material made from a member or a sufficient number ofmembers selected from the group consisting of lithium phosphates,lithium-cobalt phosphates, cobalt oxides and lithium-cobalt oxides toprovide lithium, cobalt and phosphorus in a proportion of more than 0.1mole of cobalt and more than 0.2 mole of phosphorus both per mole oflithium.
 2. The material for a lithium battery positive electrodeaccording to claim 1, wherein the organic polymer binder includes asolution of a fluororesin in an organic solvent.
 3. The material for alithium battery positive electrode according to claim 1, wherein theorganic polymer binder includes a fluororesin and an organic solvent. 4.The material for a lithium battery positive electrode according to claim1, wherein the organic polymer binder includes at least one fluororesinsoluble in an organic solvent, which is selected from the groupconsisting of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer,tetrafluoroethylene-hexafluoropropylene copolymer,tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ethercopolymer, tetrafluoroethylene-ethylene copolymer, poly(vinyl fluoride),polyhexafluoropropylene, poly(vinylidene fluoride) and vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer.
 5. Thematerial for a lithium battery positive electrode according to claim 3,wherein the organic solvent is N-methylpyrrolidone, dimethyl sulfoxide,γ-butyrolactone, propylene carbonate, ethylene carbonate ordimethylformamide.
 6. A positive electrode comprising the material for alithium battery positive electrode according to claim 1 on a conductivesheet.
 7. A method for producing a material for a lithium batterypositive electrode, which comprises coating a binder solution on asupport sheet and then drying said binder solution, said binder solutioncomprising a powdery active material made from a member or a sufficientnumber of members selected from the group consisting of lithiumphosphates, lithium-cobalt phosphates, cobalt oxides and lithium-cobaltoxides to provide lithium, cobalt and phosphorus in a proportion of morethan 0.1 mole of cobalt and more than 0.2 mole of phosphorus both permole of lithium.
 8. The method for producing a material for a lithiumbattery positive electrode according to claim 7, wherein the bindersolution includes a fluororesin solution or a fluororesin dispersion. 9.The method for producing a material for a lithium battery positiveelectrode according to claim 7, wherein the binder solution includes isa solution of a fluororesin in an organic solvent.
 10. The method forproducing a material for a lithium battery positive electrode accordingto claim 7, wherein the binder solution includes an organic solvent andat least one fluororesin selected from the group consisting oftetrafluoroethylene-perfluoroalkyl vinyl ether copolymer,tetrafluoroethylene-hexafluoropropylene copolymer,tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ethercopolymer, tetrafluoroethylene-ethylene copolymer, poly(vinyl fluoride),polyhexafluoropropylene, poly(vinylidene fluoride) and vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer.
 11. Themethod for producing a material for a lithium battery positive electrodeaccording to claim 9, wherein the organic solvent isN-methylpyrrolidone, dimethyl sulfoxide, γ-butyrolactone, propylenecarbonate, ethylene carbonate or dimethylformamide.
 12. The method forproducing a material for a lithium battery positive electrode accordingto claim 7, wherein the support sheet is a conductive sheet.
 13. Thematerial for a lithium battery positive electrode according to claim 4,wherein the organic solvent is N-methylpyrrolidone, dimethyl sulfoxide,γ-butyrolactone, propylene carbonate, ethylene carbonate ordimethylformamide.
 14. The method for producing a material for a lithiumbattery positive electrode according to claim 10, wherein the organicsolvent is N-methylpyrrolidone, dimethyl sulfoxide, γ-butyrolactone,propylene carbonate, ethylene carbonate or dimethylformamide.